Desalination system

ABSTRACT

A desalination system in the form of a submerged gas evaporator that includes a vessel, a gas delivery tube partially disposed within the vessel to deliver a gas into the vessel and a fluid inlet that provides a fluid to the vessel at a rate sufficient to maintain a controlled constant level of fluid within the vessel. A weir is disposed within the vessel adjacent the gas delivery tube to form a first fluid circulation path between a first weir end and a wall of the vessel and a second fluid circulation path between a second weir end and an upper end of the vessel. During operation, gas introduced through the tube mixes with the fluid and the combined gas and fluid flow at a high rate with a high degree of turbulence along the first and second circulation paths defined around the weir, thereby promoting vigorous mixing and intimate contact between the gas and the fluid. This turbulent flow develops a significant amount of inter facial surface area between the gas and the fluid resulting in a reduction of the required residence time of the gas within the fluid to achieve thermal equilibrium which leads to a more efficient and complete evaporation. Additionally, vapor exiting the submerged gas evaporator is condensed in a condensing unit thus precipitating vapor into a liquid for removal.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/186,459, filed on Jul. 21, 2005, the entire specification ofwhich is hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to desalination systems andliquids, and more specifically, to desalination systems includingsubmerged gas evaporators.

BACKGROUND

Desalination systems are systems that remove salt or other dissolvedsolids from water, most often to produce potable water. Currently,several methods of desalination are employed by commercial desalinationsystems. The most popular methods of commercial desalination are reverseosmosis and flash vaporization. Both of these methods have large energyrequirements and certain components that wear out frequently. Forexample, reverse osmosis systems force water through membranes and thesemembranes become clogged and torn, thus necessitating frequentreplacement. Similarly, flash vaporization systems have corrosion anderosion problems due to the spraying of hot brine within these systems.The energy requirements for a reverse osmosis system may beapproximately 6 kWh of electricity per cubic meter of water, while aflash vaporization, system may require as much as 200 kWh per cubicmeter of water. Due to the high energy inputs and frequent maintenance,desalination of water on a large scale basis has been relativelyexpensive, often more expensive than finding alternate sources ofgroundwater.

Submerged gas evaporator systems in which gas is dispersed into acontinuous liquid phase, referred to generally herein as submerged gasevaporators, are well known types of devices used to perform evaporationprocesses with respect to various constituents. U.S. Pat. No. 5,342,482,the entire specification of which is hereby incorporated by reference,discloses a common type of submerged combustion gas evaporator, in whichcombustion gas is generated and delivered though an inlet pipe to adispersal unit submerged within the liquid to be evaporated. Thedispersal unit includes a number of spaced-apart gas delivery pipesextending radially outward from the inlet pipe, each of the gas deliverypipes having small holes spaced apart at various locations on thesurface of the gas delivery pipe to disperse the combustion gas as smallbubbles as uniformly as practical across the cross-sectional area of theliquid held within the processing vessel. According to currentunderstanding within the prior art, this design provides desirableintimate contact between the liquid and the combustion gas over a largeinterfacial surface area while also promoting thorough agitation of theliquid within the processing vessel.

Because submerged gas evaporators disperse gas into a continuous liquidphase, these devices provide a significant advantage when compared toconventional evaporators when contact between a liquid stream and a gasstream is desirable. In fact, submerged gas evaporators are especiallyadvantageous when the desired result is to highly concentrate a liquidstream by means of evaporation.

However, during the evaporation process, dissolved solids within thecontinuous liquid phase become more concentrated often leading to theformation of precipitates that are difficult to handle. Theseprecipitates may include substances that form deposits on the solidsurfaces of heat exchangers within flash vaporization systems or on themembranes of reverse osmosis systems, and substances that tend to formlarge crystals or agglomerates that can block passages within processingequipment, such as the gas exit holes in the system described in U.S.Pat. No. 5,342,482. Generally speaking, feed streams that cause depositsto form on surfaces and create blockages within process equipment arecalled fouling fluids.

Deposits of precipitated solids create chemical fouling or buildup onfill or packing within conventional desalination systems that increasesavailable surface area and also create stagnant flow areas that leads tobiological fouling of these surfaces by promoting growth of bacteria andalgae. Biological growth leads to the formation of slime within adesalination system that further reduces desalination efficiency and canalso foul heat exchangers within equipment which employs the circulatingliquid from the desalination system as an evaporative medium.

These common problems adversely affect the efficiency and costs ofconventional desalination systems in that they necessitate frequentcleaning cycles and/or the addition of chemical control agents to theevaporative fluid to avoid loss of efficiency and to avoid suddenfailures within the evaporation equipment.

Additionally, most evaporation systems that rely on intimate contactbetween gases and liquids are prone to problems related to carryover ofentrained liquid droplets that form as the vapor phase disengages fromthe liquid phase. For this reason, most evaporator systems that requireintimate contact of gas with liquid include one or more devices tominimize entrainment of liquid droplets and/or to capture entrainedliquid droplets while allowing for separation of the entrained liquiddroplets from the exhaust gas flowing out of the evaporation zone.Droplets within the vapor are particularly troublesome if the process isapplied to produce potable water in that the entrained droplets containthe salts, minerals and other contaminants that were in the feed liquid.

Unlike conventional evaporators where heat and mass are transferred fromthe liquid phase as it flows over the extended surface of the heatexchangers, heat and mass transfer within submerged gas processors lakeplace at the interface of a discontinuous gas phase dispersed within acontinuous liquid phase and there are no solid surfaces upon whichdeposits can accumulate.

Submerged gas evaporators also tend to mitigate the formation of largecrystals because dispersing the gas beneath the liquid surface promotesvigorous agitation within the evaporation vessel, which is a lessdesirable environment for crystal growth than a more quiescent zone.Further, active mixing within an evaporation vessel tends to maintainprecipitated solids in suspension and thereby mitigates blockages thatare related to settling and/or agglomeration of suspended solids.

However, mitigation of crystal growth and settlement is dependent on thedegree of mixing achieved within a particular submerged gas evaporator,and not all submerged gas evaporator designs provide adequate mixing toprevent large crystal growth and related blockages. Therefore, while thedynamic renewable heat transfer surface area feature of submerged gasevaporators eliminates the potential for fouling liquids to coatextended surfaces, conventional submerged gas evaporators are stillsubject to potential blockages and carryover of entrained liquid withinthe exhaust gas flowing away from the evaporation zone.

SUMMARY OF THE DISCLOSURE

A desalination system includes an evaporator vessel, one or more tubespartially disposed within the evaporator vessel which are adapted totransport a gas into the interior of the evaporator vessel, anevaporative fluid inlet adapted to transport an evaporative fluid intothe evaporator vessel at a rate that maintains the evaporative fluidinside the evaporator vessel at a predetermined level and an exhauststack that allows vapor to flow away from the evaporator vessel. Inaddition, the desalination system evaporator includes one or more weirsthat at least partially surround the tube(s) and are at least partiallysubmerged in the evaporative fluid to create a fluid circulation pathformed by the space between the weir(s) and the walls of the evaporationvessel and gas tube(s). In one embodiment, each weir is open at bothends and forms a lower circulation gap between a first one of the weirends and a bottom wall of the evaporator vessel and an upper circulationgap between a second one of the weir ends and a normal evaporative fluidoperating level.

During operation, gas introduced through the tube or tubes mixes withthe evaporative fluid in a first confined volume formed by the weir orthe weir and a wall of the evaporation vessel and the tube(s) and thefluid mixture of gas and liquid flows at high volume with a high degreeof turbulence along the circulation path defined around the weir(s),thereby causing a high degree of mixing between the gas and theevaporative fluid and any suspended particles within the evaporativefluid. Shear forces within this two-phase or three-phase turbulent flowregion that result from the high density liquid phase overrunning thelow density gas phase create extensive interfacial surface area betweenthe gas and the evaporative fluid that favors minimum residence time formass and heat transfer between the liquid and gas phases to come toequilibrium compared to conventional gas dispersion techniques. Stillfurther, vigorous mixing created by the turbulent flow hinders theformation of large crystals of precipitates within the evaporative fluidand, because the system does not use small holes or other ports tointroduce the gas into the evaporative fluid, clogging and foulingassociated with other evaporators are significantly reduced or entirelyeliminated. Still further, the predominantly horizontal flow directionof the liquid and gas mixture over the top of the weir and along thesurface of the evaporative fluid within the evaporation vessel enablesthe gas phase to disengage from the process fluid with minimalentrainment of liquid due to the significantly greater momentum of themuch higher density liquid that is directed primarily horizontallycompared to the low density gas with a relatively weak but constantvertical momentum component due to buoyancy.

In addition, a method of desalination using a submerged gas evaporatorincludes providing a evaporative fluid to an evaporator vessel of asubmerged gas evaporator at a rate sufficient to maintain theevaporative fluid level at a predetermined level within the evaporatorvessel, supplying a gas to the evaporator vessel, and mixing the gas andevaporative fluid within the evaporator vessel by causing the gas andevaporative fluid to flow around a weir or weirs within the submergedgas processor to thereby transfer heat energy and mass between the gasand liquid phases of a mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is across-sectional view of a desalination system evaporatorconstructed in accordance with the teachings of the disclosure.

FIG. 2 is a cross-sectional view of a desalination system evaporatorincluding a baffle.

FIG. 3 is a cross-sectional view of a desalination system evaporatorhaving a tubular shaped weir.

FIG. 4 is a top plan view of the desalination system evaporator of FIG.3.

FIG. 5 is a cross-sectional view of a desalination system evaporatorconnected to a source of waste heat.

FIG. 6 is a cross-sectional view of a desalination system including acooling/condensing unit.

FIG. 7 is a cross-sectional view of a desalination system evaporatorhaving multiple weirs and multiple gas inlet tubes.

DETAILED DESCRIPTION

The performance of desalination systems according to the disclosuredepends on the moisture content and temperature of the gas and thethermodynamic properties of the evaporative fluid, which are usuallyambient air and water. As with conventional desalination systems,equations developed by Merkel that are based the enthalpy potentialdifference between the evaporative fluid and air, may be used to closelydefine the performance of a desalination system that is constructedaccording to the invention for a particular application. Desalinationsystems according to the disclosure can be substituted for conventionaldesalination systems. Conventional means of controlling the flow ofevaporative fluid through the desalination system may be employed.Likewise, conventional means of controlling desalination systems to meetthe requirements of a particular desalination system application may beemployed. Multiple desalination systems according to the invention maybe connected in series or parallel configurations to meet thedesalination demand of a particular application.

Referring to FIG. 1, a desalination system evaporator 10, includes afan/blower 20 and a gas supply tube or gas inlet tube 22 having spargeor gas exit ports 24 at or near an end 26 thereof. The gas inlet tube 22supplies gas under positive pressure to an evaporator vessel 30 having abottom wall 31 and an evaporative fluid outlet port 32. An evaporativefluid inlet port 34 is disposed in one side of the vessel 30 and enablesan evaporative fluid 35 to be provided into the interior of theevaporator vessel 30. Additionally, a weir 40, which is illustrated inFIG. 1 as a flat or solid plate member having a first or lower end 41and a second or upper end 42, is disposed within the evaporator vessel30 adjacent the gas inlet tube 22. Although the evaporator vessel 30 andgas inlet tube 22 are generally shown herein as cylindrical in shape,one skilled in the art will realize that many other shapes may beemployed for these elements. The weir 40 defines and separates twovolumes 70 and 71 within the evaporator vessel 30. As illustrated inFIG. 1, a gas exit port 60 disposed in the top of the vessel 30 enablesgas (vapor) to exit from the interior of the evaporator vessel 30.Disposed near a junction of the gas exit port 60 and the evaporatorvessel 30 is a demister 61. The demister 61 removes droplets ofevaporative fluid that are entrained in the gas phase as the gasdisengages from the liquid phase at the surface 80 of the liquid. Thedemister 61 may be a vane-type demister, a mesh pad-type demister, orany combination of commercially available demister elements. Further, avane-type demister may be provided having a coalescing filter to improvedemisting performance. The demister 61 may be mounted in any orientationand adapted to a particular evaporator vessel 30 including, but notlimited to, horizontal and vertical orientations.

In the desalination system evaporator of FIG. 1, the fan/blower 20 issupplied with gas through a line 51. Moreover, the evaporative fluid 35may be supplied through the fluid inlet 34 by a pump (not shown inFIG. 1) at a rate sufficient to maintain a surface 80 of the evaporativefluid 35 within the evaporator vessel 30 at a predetermined level, whichmay be set by a user. A level sensor and control (not shown in FIG. 1)may be used to determine and control the rate that the evaporative fluid35 is supplied through the inlet port 34.

As illustrated in FIG. 1, the weir 40 is mounted within the evaporatorvessel 30 to form a lower circulation gap 36 between the first end 41 ofthe weir 40 and the bottom wall 31 of the evaporator vessel 30 and toform an upper circulation gap 37 between the second end 42 of the weir40 and the surface 80 of the evaporative fluid 35 (or a top wall of theevaporator vessel 30). As will be understood, the upper end 42 of theweir 40 is preferably set to be at or below the surface level 80 of theevaporative fluid 35 when the evaporative fluid 35 is at rest (i.e.,when no gas is being introduced into the evaporator vessel 30 via thegas inlet tube 22). As illustrated in FIG. 1, the weir 40 also definesand separates the confined volume or space 70 in which the sparge ports24 are located from the volume or space 71. If desired, the weir 40 maybe mounted to the evaporator vessel 30 via welding, bolts or otherfasteners attached to internal side walls of the evaporator vessel 30.

During operation, gas from the line 51 is forced to flow under pressureinto and through the gas inlet tube 22 to the sparge or exit ports 24.The gas exits the gas inlet tube 22 through the sparge ports 24 into theconfined volume 70 formed between the weir 40 and the gas inlet tube 22,causing the gas to be dispersed into the continuous liquid phase of theevaporative fluid within the evaporator vessel 30. Generally speaking,gas exiting from the sparge ports 24 mixes with the liquid phase of theevaporative fluid within the confined volume 70 and causes a high volumeflow pattern to develop around the weir 40. The velocity of the flowpattern and hence the turbulence associated with the flow pattern ishighest within the confined volume 70 and at the locations where theevaporative liquid flows through the upper gap 37 and the lower gap 36of the weir 40. The turbulence within the confined volumes 70 and 71significantly enhances the dispersion of the gas into the evaporativefluid which, in turn, provides for efficient heat and mass transferbetween the gas and the evaporative fluid. In particular, after exitingthe sparge ports 24, the gas is dispersed as a discontinuous phase intoa continuous liquid phase of the evaporative fluid forming a gas/liquidmixture within the confined volume 70. The mass per unit volume of thegas/liquid mixture in the confined volume 70 is significantly less thanthat of the average mass per unit volume of the continuous liquid phaseof the evaporative fluid in the volume 71, due to the large differencein mass per unit volume of the liquid compared to the gas, typically onthe order of approximately 1000 to 1. This difference in mass per unitvolume creates a difference in static hydraulic pressure between thegas/liquid mixture in the confined volume 70 and the liquid phase in thevolume 71 at all elevations. This imbalance in static hydraulic pressureforces the evaporative fluid to flow from the higher pressure region,i.e., the volume 71, to the lower pressure region, i.e., the confinedvolume 70, at a rate that overcomes the impressed static hydraulicpressure imbalance and creates flow upward through the confined volume70.

Put another way, the dispersion of gas into the evaporative fluid 35within the confined volume 70 at the sparge ports 24 develops acontinuous flow pattern that draws evaporative fluid 35 under the bottomedge 41 of the weir 40 through the lower circulation gap 36, and causesthe mixture of gas and evaporative fluid 35 to move through the confinedvolume 70 and toward the surface 80 of the evaporative fluid 35. Nearthe surface 80, the gas/liquid mixture reaches a point of balance atwhich the imbalance of static hydraulic pressure is eliminated.Generally speaking, this point is at or near the tipper circulation gap37 formed between the second end 42 of the weir 40 and the evaporativefluid surface 80. At the balance point, the force of gravity, whichbecomes the primary outside force acting on the gas/fluid mixture,gradually reduces the vertical momentum of the gas/liquid mixture tonear zero. This reduced vertical momentum, in turn, causes thegas/liquid mixture to flow in a predominantly horizontal direction overthe second end 42 of the weir 40 (through the circulation gap 37 definedat or near the surface 80 of the evaporative fluid 35) and into theliquid phase of the evaporative fluid 35 within the volume 71.

This flow pattern around and over the weir 40 affects the dispersion ofthe gas into the continuous liquid phase of the evaporative fluid 35and, in particular, thoroughly agitates the continuous liquid phase ofthe evaporative fluid 35 within the evaporator vessel 30 while creatinga substantially horizontal flow pattern of the gas/liquid mixture at andnear the surface 80 of the continuous liquid phase of the evaporativefluid 35. This horizontal flow pattern significantly mitigates thepotential for entrained liquid droplets to he carried vertically upwardalong with the dispersed gas phase as the dispersed gas phase risesthrough the liquid phase due to buoyancy and finally disengages from thecontinuous liquid phase of the evaporative fluid at the surface 80 ofthe evaporative fluid 35.

Also, the mixing action created by the induced flow of liquid andliquid/gas mixtures within both the confined volume 70 and the volume 71hinders the formation of large crystals of precipitates (e.g., salt),which generally requires a quiescent environment. By selectivelyfavoring the production of relatively small incipient particles ofprecipitates, the mixing action within evaporator vessel 30 helps toensure that suspended particles formed in the submerged gas evaporationprocess may be maintained in suspension within the liquid phasecirculating around the weir 40, which effectively mitigates theformation of blockages and fouling within the desalination systemevaporator 10. Likewise, because relatively small particles that arereadily maintained in suspension are formed through precipitation, theefficiency of the evaporator is improved over conventional evaporationsystems in terms of freedom from clogging and fouling and the degree towhich the feed liquid may be concentrated.

In addition, as the circulating liquid phase within volume 71 approachesthe bottom wall 31 of the vessel 30, the liquid phase is forced to flowin a predominantly horizontal direction and through the lower gap 36into the confined volume 70. This predominantly horizontal flow patternnear the bottom wall 31 of the evaporator vessel 30 creates a scouringaction at and above the interior surface of the bottom wall 31 whichmaintains particles of solids including precipitates in suspensionwithin the circulating liquid while the desalination system isoperating. The scouring action at and near the bottom wall 31 of theevaporator vessel 30 also provides means to re-suspend settled particlesof solids whenever the desalination system is re-started after havingbeen shutdown for a period of time sufficient to allow suspendedparticles to settle on or near the bottom wall 31.

As is known, submerged gas evaporation is a process that affectsevaporation by contacting a gas with a liquid or liquid mixture, whichmay be a compound, a solution or slurry. Within a submerged gasevaporator heat and mass transfer operations occur simultaneously at theinterface formed by the dynamic boundaries of the discontinuous gas andcontinuous liquid phases. Thus, all submerged gas evaporators includesome method to disperse gas within a continuous liquid phase. The systemshown in FIG. 1 however integrates the functions of dispersing the gasinto the liquid phase, providing thorough agitation of the liquid phase,and mitigating entrainment of liquid droplets with the gas phase as thegas disengages from the liquid. Additionally, the turbulence and mixingthat occurs within the evaporator vessel 30 due to the flow patterncreated by dispersion of gas into liquid within the confined volume 70reduces the formation of large crystals of precipitates and/or largeagglomerates of smaller particles within the evaporator vessel 30.

FIG. 2 illustrates a second embodiment of a desalination systemevaporator 110, which is very similar to the desalination systemevaporator 10 of FIG. 1 and in which elements shown in FIG. 2 areassigned reference numbers being exactly 100 greater than thecorresponding elements of FIG. 1. Unlike the device of FIG. 1, thedesalination system evaporator 110 includes a baffle or a shield 138disposed within the evaporator vessel 130 at a location slightly aboveor slightly below the evaporative fluid surface 180 and above the secondend 142 of the weir 140. The baffle or shield 138 may be a generallyflat plate shaped and sized to conform generally to the horizontalcross-sectional area of the confined volume 170. Additionally, ifdesired, the baffle 138 may be mounted to any of the gas inlet tube 122,the evaporator vessel 130 or the weir 140. The baffle 138 augments theforce of gravity near the balance point by presenting a physical barrierthat abruptly and positively eliminates the vertical components ofvelocity and hence, momentum, of the gas/liquid mixture, therebyassisting the mixture to flow horizontally outward and over the weir 140at the upper circulation gap 137. The baffle enhances mitigation ofentrained liquid droplets within the gas phase as the gas disengagesfrom the liquid phase. Furthermore, the blower 120 is disposed on thegas exit port 160 in this embodiment thereby providing gas to theevaporation vessel 130 under negative pressure, i.e., via suction.

As will be understood, the weirs 40 and 140 of FIGS. 1 and 2 may begenerally flat plates or may be curved plates that surround the gastubes 22, 122 and/or that extend across the interior of the evaporatorvessel 30 between different, such as opposite, sides of the evaporatorvessel 30. Basically, the weirs 40 and 140 create a wall within theevaporator vessels 30, 130 defining and separating the volumes 70 and 71(and 170 and 171). While the weirs 40 and 140 are preferably solid innature they may, in some cases, be perforated, for instance, with slotsor holes to modify the flow pattern within the evaporator vessel 30 or130, or to attain a particular desired mixing result within the volume71 or 171 while still providing a substantial barrier between thevolumes 70 and 71 or 170 and 171. Additionally, while the weirs 40 and140 may extend across the evaporator vessels 30 and 130 between oppositewalls of the evaporator vessels 30 and 130, they may be formed into anydesired shape so long as a substantial vertical barrier is formed toisolate one volume 70 (or 170) closest to the gas inlet tube 22 from thevolume 71 (or 171) on the opposite side of the weir 40, 140.

FIG. 3 illustrates a cross-sectional view of a further desalinationsystem evaporator 210 having a weir 240 that extends around a gas inlettube 222. The desalination system evaporator 210, generally speaking,has evaporative capacity equivalent to approximately 10,000 gallons perday on the basis of evaporating water from an evaporative liquid. Afan/blower (not shown in FIG. 3) delivers hot gas which could beapproximately 12,300 actual cubic feet per minute (acfm) at 1,400° F. tothe gas inlet tube 222. While the dimensions of the desalination systemevaporator 210 are exemplary only, the ratios between these dimensionsmay serve as a guide for those skilled in the art to achieve a desirablebalance between three desirable evaporation results including: 1)preventing the formation of large crystals of precipitates and/oragglomerates of solid particles while maintaining solid particles as ahomogeneous suspension within the process liquid by controlling thedegree of overall mixing within vessel 230; 2) enhancing the rates ofheat and mass transfer by controlling the turbulence and henceinterfacial surface area created between the gas and liquid phaseswithin confined volume 270; and 3) mitigating the potential ofentraining liquid droplets in the gas as the gas stream disengages fromthe liquid phase at the liquid surface 280 by maintaining a desirableand predominately horizontal velocity component for the gas/liquidmixture flowing outward over the second end 242 of the weir 240 andalong the surface of the evaporative liquid 280 within evaporator vessel230. As illustrated in FIG. 3, the desalination system evaporator 210includes an evaporator vessel 230 with a dished bottom having aninterior volume and a vertical gas inlet tube 222 at least partiallydisposed within the interior volume of the evaporator vessel 230. Inthis case, the gas inlet tube 222 has a diameter of approximately 20inches and the overall diameter of the evaporation vessel 230 isapproximately 120 inches, but these diameters may be more or less basedon the design capacity and desired process result as relates to both gasand liquid flow rates and the type of combustion device (not shown inFIG. 3) supplying hot gas to the desalination system evaporator 320.

In this example the weir 240 has a diameter of approximately 40 incheswith vertical walls approximately 26 inches in length. Thus, the weir240 forms an annular confined volume 270 within the evaporation vessel230 between the inner wall of the weir 240 and the outer wall of the gasinlet tube 222 of approximately 6.54 cubic feet. In the embodiment ofFIG. 3, twelve sparge ports 224 are disposed near the bottom of the gasinlet tube 222. The sparge ports 224 are substantially rectangular inshape and are, in this example, each approximately 3 inches wide by 7¼inches high or approximately 0.151 ft² in area for a combined total areaof approximately 1.81 ft² for all twelve sparge ports 224.

As will be understood, the gas exits the gas inlet tube 222 through thesparge ports 224 into a confined volume 270 formed between the gas inlettube 222 and a tubular shaped weir 240. In this case, the weir 240 has acircular cross-sectional shape and encircles the lower end of the gasinlet tube 222. Additionally, the weir 240 is located at an elevationwhich creates a lower circulation gap 236 of approximately 4 inchesbetween a first end 241 of the weir 240 and a bottom dished surface 231of the evaporator vessel 230. The second end 242 of the weir 240 islocated at an elevation below a normal or at rest operating level of theevaporative fluid within the evaporator vessel 230. Further, a baffle orshield 238 is disposed within the evaporator vessel 230 approximately 8inches above the second end 242 of the weir 240. The baffle 238 iscircular in shape and extends radially outwardly from the gas inlet tube222. Additionally, the baffle 238 is illustrated as having an outerdiameter somewhat greater than the outer diameter of the weir 240 which,in this case, is approximately 46 inches. However, the baffle 238 mayhave the same, a greater or smaller diameter than the diameter of theweir 240 if desired. Several support brackets 233 are mounted to thebottom surface 231 of the evaporator vessel 230 and are attached to theweir 240 near the first end 241 of the weir 240. Additionally, a gasinlet tube stabilizer ring 235 is attached to the support brackets 233and substantially surrounds the bottom end 226 of the gas inlet lube 222to stabilize the gas inlet tube 222 during operation.

During operation of the desalination system evaporator 210, the gasesare ejected through the sparge ports 224 into the confined volume 270between the outer wall of the gas inlet tube 222 and the inside wall ofthe weir 242 creating a mixture of gas and liquid within the confinedvolume 270 that is significantly reduced in bulk density compared to theaverage bulk density of the fluid located in the volume 290 outside ofthe wall of the weir 240. This reduction in bulk density of thegas/liquid mixture within confined volume 270 creates an imbalance inhead pressure at all elevations between the surface 280 of theevaporative liquid within the evaporator vessel 230 and the first end241 of the weir 240 when comparing the head pressure within the confinedvolume 270 and head pressure within the volume 290 outside of the wallof the weir 240 at equal elevations. The reduced head pressure withinthe confined volume 270 induces a flow pattern of liquid from the higherhead pressure regions of volume 290 through the circulation gap 236 andinto the confined volume 270. Once established, this induced flowpattern provides vigorous mixing action both within the confined volume270 and throughout the volume 290 as evaporative liquid from the surface280 and all locations within the volume 290 is drawn downward throughthe circulation gap 236 and upward due to buoyancy through the confinedvolume 270 where the gas/liquid mixture flows outward over the secondend 242 of the weir 240 and over the surface 280 confined within theevaporator vessel 230.

Within confined volume 270, the induced flow pattern and resultantvigorous mixing action creates significant shearing forces that areprimarily based on the gross difference in specific gravity and hencemomentum vectors between the liquid and gas phases at all points on theinterfacial surface area of the liquid and gas phases. The shearingforces driven by the significant difference in specific gravity betweenthe liquid and gas phases, which is, generally speaking, of a magnitudeof 1000:1 liquid to gas, cause the interfacial surface area between thegas and liquid phases to increase significantly as the average volume ofeach discrete gas region within the mixture becomes smaller and smallerdue to the shearing force of the flowing liquid phase. Thus, as a resultof the induced flow pattern and the associated vigorous mixing withinthe confined area 270, the total interfacial surface area increases asthe gas/liquid mixture flows upward within confined volume 270. Thisincrease in interfacial surface area or total contact area between thegas and liquid phases favors increased rates of heat and mass transferbetween constituents of the gas and liquid phases as the gas/liquidmixture flows upward within confined volume 270 and outward over thesecond end 242 of the weir 240.

At the point where gas/liquid mixture flowing upward within confinedvolume 270 reaches the elevation of tire evaporative fluid surface 280and having passed beyond the second edge 242 of the weir 240, thedifference in head pressure between the gas/liquid mixture within theconfined volume 270 and the liquid within volume 290 fluid iseliminated. Absent the driving force of differential head pressure andthe confining effect of the weir 240, gravity and the resultant buoyancyof the gas phase within the liquid phase become the primary outsideforces affecting the continuing flow patterns of the gas/liquid mixtureexiting the confined space 270. The combination of the force of gravityand the impenetrable barrier created by the baffle 238 eliminates thevertical velocity and momentum components of the flowing gas/liquidmixture at or below the elevation of the bottom of the baffle 238 andcauses the velocity and momentum vectors of the flowing gas/liquidmixture to be directed outward through the gap 239 created by the secondend 242 of the weir 240 and the bottom surface of the baffle 238 anddownwards near the surface 280 within the evaporator vessel 230 causingthe continuing flow pattern of the gas/liquid mixture to assume apredominantly horizontal direction. As the gas/liquid mixture flowsoutwards in a predominantly horizontal direction, the horizontalvelocity component continually decreases causing a continual reductionin momentum and a reduction of the resultant shearing forces acting atthe interfacial area within the gas/liquid mixture. The reduction inmomentum and resultant shearing forces allows the force of buoyancy tobecome the primary driving force directing the movement of thediscontinuous gas regions within the gas/liquid mixture, which causesdiscrete and discontinuous regions of gas to coalesce and ascendvertically within the continuous liquid phase. As the ascending gasregions within the gas/liquid mixture reach the surface 280 of theevaporative liquid within the evaporator vessel 230, buoyancy causes thediscontinuous gas phase to break through the surface 280 and to coalesceinto a continuous gas phase that is directed upward within the confinesof the evaporator vessel 230 and into the vapor exhaust duct 260 underthe influence of the differential pressure created by the fan/blower(not shown in FIG. 3) supplying gas to the desalination systemevaporator 210.

FIG. 4 is a top plan view of the desalination system evaporator 210 ofFIG. 3 illustrating the tubular nature of the weir 240. Specifically,the generally circular gas inlet tube 222 is centrally located and issurrounded by the stabilizer ring 235. In this embodiment, thestabilizer ring 235 surrounds the gas inlet tube 222 and essentiallyrestricts any significant lateral movement of the gas inlet tube 222 dueto surging or vibration such as might occur upon startup of the system.While the stabilizer ring 235 of FIG. 4 is attached to the supportbrackets 233 at two locations, more or fewer support brackets 233 maybeemployed without affecting the function of the desalination systemevaporator 210. The weir 240, which surrounds the gas inlet tube 222 andthe stabilizer ring 235, and is disposed co-axially to the gas inlettube 222 and the stabilizer ring 235, is also attached to, and issupported by the support brackets 233. In this embodiment, the confinedvolume 270 is formed between the weir 240 and the gas inlet tube 222while the second volume 290 is formed between the weir 240 and the sidewalls of the evaporator vessel 230. As will be understood, in thisembodiment, the introduction of the gas from the exit ports 224 of thegas inlet tube 220 causes evaporative fluid to flow in an essentiallytoroidal pattern around the weir 240.

Some design factors relating to the design of the desalination systemevaporator 210 illustrated in FIGS. 3 and 4 are summarized below and maybe useful in designing larger or smaller desalination systemevaporators. The shape of the cross sectional area and length of the gasinlet tube is generally set by the allowable pressure drop, theconfiguration of the evaporator vessel, the costs of forming suitablematerial to match the desired cross sectional area, and thecharacteristics of the fan/blower that is coupled to the desalinationsystem evaporator. However, it is desirable that the outer wall of thegas inlet tube 222 provides adequate surface area for openings of thedesired shape and size of the sparge ports which in turn admit the gasto the confined volume 290. For a typical desalination system evaporatorthe vertical distance between the top edge 242 of the weir 240 and thetop edge of the sparge ports should be not less than about 6 inches andpreferably is at least about 17 inches. Selecting the shape and, moreparticularly, the size of the sparge port 224 openings is a balancebetween allowable pressure drop and the initial amount of interfacialarea created at the point where the gas is dispersed into the flowingliquid phase within confined volume 290. The open area of the spargeports 224 is generally more important than the shape, which can he mostany configuration including, hut not limited to, rectangular,trapezoidal, triangular, round, oval. In general, the open area of tiresparge ports 224 should be such that the ratio of gas flow to totalcombined open area of all sparge ports should at least be in the rangeof 1,000 to 18,000 acfm per ft², preferably in the range of 2,000 to8,000 acfm/ft² and more preferably in the range of 2,000 to 8,000acfm/ft², where acfm is referenced to the operating temperature withinthe gas inlet tube. Likewise, the ratio of the gas flow to the crosssectional area of the confined volume 270 should be at least in therange of 400 to 10,000 scfm/ft², preferably in the range of 500 to 4,000scfm/ft² and more preferably in the range of 500 to 2,000 scfm/ft².Additionally, the ratio of the cross sectional area of the evaporatorvessel 230 to the cross sectional area of the confined volume 270((CSA_(vessel)) is preferably in the range from three to one (3.0:1) totwo-hundred to one (200:1), is more preferably in the range from eightto one (8.0:1) to one-hundred to one (100:1) and is highly preferably inthe range of about ten to one (10:1) to fourteen to one (14:1). Theseratios are summarized in the table below. Of course, in somecircumstances, other ratios for these design criteria could be used aswell or instead of those particularly described herein.

TABLE 1 Preferred Ratios Embodiment Acceptable Range Preferred Rangeacfm:Total/CSA_(sparge ports) 2,000-8,000 acfm/ft² 1,000-18,000 acfm/ft²2,000-10,000 acfm/ft² scfm:/CSA_(confined volume)   500-2,000 scfm/ft²  400-10,000 scfm/ft²   500-4,000 scfm/ft²CSA_(vessel)/CSA_(confined volume): 10:1-14:1 3.0:1-200:1 8.0:1-100:1

Turning now to FIG. 5, a desalination system evaporator is shown whichis similar to the desalination system evaporator of FIG. 1, and in whichlike components are labeled with numbers exactly 300 greater than thecorresponding elements of FIG. 1. The desalination system evaporator 310of FIG. 5 receives hot gases directly from an external source. The hotgases supplied by the external source may include gases having a widerange of temperature and/or specific components and these hot gases maybe selected by one skilled in the art to achieve any specific rate ofevaporation.

FIG. 6 illustrates a desalination system evaporator 510 which is similarto the desalination system evaporators of FIGS. 1, 2 and 5, in whichlike elements are labeled with reference numbers exactly 500 greaterthan those of FIG. 1. However, the desalination system evaporator 510 isconnected to a condensing unit 600 thereby forming a desalinationsystem. The condensing unit 600 includes a condensing vessel 610 havinga cooling fluid input port 612 and a cooling fluid exit port 614. Vaportravels from the desalination system evaporator 510 through the gas exitport 560 along a transfer tube 616 and into a condensing tube 618 thatis partially disposed within the condensing vessel 610. Within thecondensing vessel 610, the condensing tube 618 is partially submerged ina cooling fluid which has a surface 680. The submerged portion of thecondensing tube 618 allows heat transfer from the vapor within thecondensing tube 618 to the cooling fluid, thus allowing the vapor thevapor to condense. Accordingly, the condensed liquid accumulates at thelowest points of the condensing tube where the condensed liquid may beremoved via one or more removal valves 622.

The embodiment of a desalination system evaporator 710 shown in FIG. 7includes multiple gas tubes 722 and multiple weirs 740. The evaporatorvessel 730 may include more than one gas tube 722 and/or more than oneweir 740 to increase desalinating capability without a significantincrease in the size of the evaporator vessel 710.

In a desalination system, the evaporative fluid introduced into theevaporation vessel 510 is generally salt water or brine. Concentratedbrine may be removed through the outlet port 532. As hot gas isintroduced through the supply tube 522 and mixed with the brine, watervapor is absorbed by the hot gas and carried out of the evaporationvessel through the gas exit port 560. Through the positive (or negative)pressure imparted to the hot gas via the fan/blower, the vapor is forced(or drawn) through the transfer pipe 616 and into the condensing vessel610. This movement may be facilitated by one or more fans or pumpslocated in the gas exit 624. Regardless, as the vapor traverses thecondensing tube 618, the vapor cools as a result of heat transferthrough the condensing tube 618 walls to the cooling fluid. As a resultof vapor cooling, the ability of the vapor to retain water will decreaseto the point of saturation. Thereafter, water will precipitate out ofthe vapor and collect in the condensing tube 618. The amount ofprecipitated water will depend on the amount of cooling performed in theevaporation vessel and the entry temperature of the vapor. Theprecipitated water may be removed from the condensing tube through thewafer removal valves 622.

The embodiment of a desalination system evaporator 710 shown in FIG. 8includes multiple gas tubes 722 and multiple weirs 740. The evaporatorvessel 730 may include more than one gas tube 722 and/or more than oneweir 740 to increase cooling capability without a significant increasein the size of the desalination system evaporator 710.

The desalination system described above has many advantages over knowndesalination systems. For example, a desalination system as describedabove has virtually no moving parts and no heat transfer surfaces in theevaporation unit. Thus, maintenance and replacement are greatly reduced.The disclosed desalination system is scalable to accommodate virtuallyany required fresh water output. Additionally, readily available heatsources and brine sources may be used. For example, solar energy couldbe used to heat the input gas and seawater could be used for the brine.When operated on solar energy the energy requirement would besignificantly less than that that for conventional systems. In addition,the seawater could be used as both the cooling fluid in the condensingvessel and as the evaporative liquid in the evaporator vessel. These andmany other advantages may be realized with the desalination systemdescribed herein.

Desalination systems according to the disclosure operate at higherpercentages of suspended solids and/or the ability to use cooling fluidswith higher concentrations of dissolved solids (due in part to theturbulent flow described above). Thus, desalination systems according tothe disclosure can be used to desalinate brackish water that has veryhigh concentrations of contaminants and also require less preventativemaintenance (i.e., cleaning due to chemical residue buildup and/orprecipitate coating of internal surfaces) than conventional desalinationsystems.

It will be understood that, because the weir and gas dispersionconfigurations within desalination system evaporators illustrated in theembodiments of FIGS. 1-8 provide for a high degree of mixing, inducedturbulent flow and the resultant intimate contact between liquid and gaswithin the confined volumes 70, 170, 270, etc., the desalination systemevaporators of FIGS. 1-8 create a large interfacial surface area for theinteraction of the evaporative fluid and the gas provided via die gasinlet tube, leading to very efficient heat and mass transfer between gasand liquid phases. Furthermore, the use of the weir and, if desired, thebaffle, to cause a predominantly horizontal flow pattern of thegas/liquid mixture at the surface of the evaporative fluid mixturemitigates or eliminates the entrainment of droplets of evaporative fluidwithin the exhaust gas. Still further, the high degree of turbulent flowwithin the evaporator vessel mitigates or reduces the formation of largecrystals or agglomerates and maintains the mixture of solids and liquidswithin the evaporator vessel in a homogeneous state to prevent or reducesettling of precipitated solids. This factor, in turn, reduces oreliminates the need to frequently clean the evaporator vessel and allowsthe evaporation to proceed to a very high state of concentration bymaintaining precipitates in suspension. In the event that such solids doform, however, they may be removed via the outlet port 32 (FIG. 1) usinga conventional valve arrangement.

While several of different types of desalination system evaporatorshaving different weir configurations are illustrated herein, it will beunderstood that the shapes and configurations of the components,including the weirs, baffles and gas entry ports, used in these devicescould be varied or altered as desired. Thus, for example, while the gasinlet tubes are illustrated as being circular in cross section, thesetubes could be of any desired cross sectional shape including, forexample, square, rectangular, oval, etc. Additionally, while the weirsillustrated herein have been shown as flat plates or as tubular membershaving a circular cross-sectional shape, weirs of other shapes orconfigurations could be used as well, including weirs having a square,rectangular, oval, or other cross sectional shape disposed around a fireor other gas inlet tube, weirs being curved, arcuate, or multi-facetedin shape or having one or more walls disposed partially around a fire orgas inlet tube, etc. Also, the gas entry ports shown as rectangular mayassume most any shape including trapezoidal, triangular, circular, oval,or triangular.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes in the methods and apparatusdisclosed herein may be made without departing from the scope of theinvention, which is defined in the appended claims.

1. A desalination system comprising: a desalination system evaporatorcomprising: a first vessel having an interior adapted to hold a liquid;a tube disposed within the first vessel and adapted to transport a gasinto the interior of the first vessel; a weir disposed within the firstvessel adjacent the tube in a manner that defines a confined volumebetween the tube and the weir; a vapor pipe adapted to transport exhaustvapor from the interior of the first vessel; and a liquid inlet adaptedto supply a liquid to the interior of the first vessel; wherein the weirincludes a first weir end and a second weir end and is disposed withinthe vessel to define a first circulation gap between the first weir endand a first wall of the first vessel and to define a second circulationgap between the second weir end and a second wall of the first vesselwhich enables liquid within the first vessel to flow through the firstand second circulation gaps when gas is introduced into the first vesselfrom the tube; and a condensing unit comprising: a second vessel havingan inlet and an outlet for supplying a cooling fluid; a vapor pipepassing through the second vessel and at least partially surrounded bythe cooling fluid within the second vessel; a liquid collection and exitport for removing condensed liquid from the second vessel.
 2. Thedesalination system of claim 1, further including a baffle disposed inthe first vessel proximate the second circulation gap and generallyperpendicular to the weir.
 3. The desalination system of claim 2,wherein the liquid is one of seawater and brine.
 4. The desalinationsystem of claim 2, wherein condensed liquid is periodically removedthrough a removal port in the second vessel.
 5. The desalination systemof claim 1, wherein the tube includes a gas exit disposed below asurface of the liquid when liquid is disposed within the first vessel.6. The desalination system of claim 5, further including a plurality ofgas exits disposed in the tube, wherein each gas exit is substantiallyrectangular in shape.
 7. The desalination system of claim 6, wherein aratio of gas flow in actual cubic feet per minute (acfm) out of the tubeas measured at the operating temperature of the gas flowing within thetube to a cross sectional area of gas exit slots in the tube is in therange of approximately 1,000 acfm/ft² to approximately 18,000 acfm/ft².8. The desalination system of claim 6, wherein the ratio of gas flow inactual cubic feet per minute (acfm) out of the tube as measured at theoperating temperature of the gas within the lube to the cross sectionalarea of gas exit slots in the tube is in the range of approximately2,000 acfm/ft² to approximately 8,000 acfm/ft².
 9. The desalinationsystem of claim 1, further including a reinforcing plate attached to thefirst vessel and attached to the weir.
 10. The desalination system ofclaim 9, further including a stabilizer ring attached to the reinforcingplate and disposed between the tube and the weir.
 11. The desalinationsystem of claim 1, wherein a ratio of gas flow in standard cubic feetper minute (scfm) out of the tube to a cross sectional area of aconfined volume in the first vessel is in the range of approximately 400scfm/ft² to approximately 10,000 scfm/ft².
 12. The desalination systemof claim 11, wherein the ratio of gas flow in scfm out of the tube to across sectional area of the confined volume is in the range ofapproximately 500 scfm/ft² to approximately 2,000 scfm/ft².
 13. Thedesalination system of claim 1, wherein a ratio of a cross sectionalarea of the first vessel to a cross sectional area of the confinedvolume is in the range of approximately 3 to 1 to approximately 200to
 1. 14. The desalination system of claim 13, wherein the ratio of across sectional area of the confined volume to a cross sectional area ofthe first vessel is in the range of approximately 10 to 1 toapproximately 14 to
 1. 15. The desalination system of claim 1, whereinthe weir comprises a tubular member disposed around the tube.
 16. Thedesalination system of claim 15, wherein the tubular member is circularin cross section.
 17. The desalination system of claim 15, wherein thetubular member is disposed co-axial to the tube.
 18. The desalinationsystem of claim 1, wherein the weir comprises a generally flat platemember.
 19. The desalination system of claim 1, wherein the tube isconnected to a source of waste heat.
 20. The desalination system ofclaim 1 wherein the gas is supplied to the first vessel under positivepressure.
 21. The desalination system of claim 1 wherein the gas issupplied to the first vessel under negative pressure.
 22. Thedesalination system of claim 1 further comprising a demister to removeentrained liquid droplets from the gas before the gas exits the firstvessel.
 23. The desalination system of claim 22 wherein the demister isa vane-type demister.
 24. The desalination system of claim 22 whereinthe demister is a mesh pad-type demister.
 25. The desalination system ofclaim 22 wherein the demister is a combination of a vane-type demisterand a mesh pad-type demister.
 26. The desalination system of claim 22wherein the demister is a vane-type demister having a coalescing filter.27. The desalination system of claim 1 further comprising a plurality ofgas tubes in the first vessel.
 28. The desalination system of claim 1further comprising a plurality of weirs in the first vessel.
 29. Thedesalination system of claim 1 further comprising a plurality of blowersin the first vessel.
 30. A method of removing salt from an evaporativefluid in a desalination system evaporator having a weir disposed withinan evaporator vessel, the weir defining first and second volumes withinthe evaporator vessel and a gas delivery tube extending into theevaporator vessel into the first volume, comprising: supplying anevaporative fluid to the evaporator vessel at a rate sufficient tomaintain an evaporative fluid surface level in the evaporator vesselnear or above a first end of the weir; providing gas through the gasdelivery tube to force the gas through an exit in the gas delivery tubeto cause mixing of the gas and the evaporative fluid within the firstvolume by creating a circular flow of evaporative fluid from the firstvolume around the first end of the weir into the second volume and fromthe second volume around a second end of the weir and into the firstvolume; removing exhaust gases through an exhaust stack in theevaporator vessel; and condensing evaporative fluid vapor containedwithin the removed exhaust gases.
 31. The method of claim 33, furtherincluding removing evaporative fluid with suspended solid particulatefrom the evaporator vessel.